The preparation of the radionuclide fluorine-18 is known in the art. Of the various methods known in the art whereby fluorine-18 can be formed, the neon-20 (deuteron, alpha particle) is preferred. In this reaction, a quantity of neon-20 gas molecules enclosed within a reaction zone is irradiated with energetic deuteron particles to form the radionuclide fluorine-18 and alpha particles as reaction products. This reaction also produces a number of radiocontaminants, principally .sup.22 Na which is produced by the reactions .sup.21 Ne (d,n).sup.22 Na and .sup.22 Ne (d,2n).sup.22 Na. Obviously, when utilizing other gases, e.g. oxygen, to prepare fluorine-18 corresponding radiocontaminants are produced. Further, deuterons and secondary neutrons react with the metal foil cover and internal walls of the cyclotron target to form additional contaminants. For example, wherein the target is lined with nickel, the reactions .sup.60 Ni (d,n).sup.61 Ni (d,2n).sup.64 Cu take place as well as the formation of shorterlived radioisotopes of copper and neutron activation products of the nickel itself. These radiocontaminants adhere to the walls of the reaction vessel as does the desired fluorine-18. The problem therefore has been how best to recover fluorine-18 in an ultrapure form.
One method of recovering fluorine-18 produced under the above-described conditions has been to disassemble the reactor and wash the product from the interior walls of the reaction chamber. This method suffers two disadvantages, i.e. the washing also removes the radiocontaminants which must then be separated chemically or physically from the product and the separation and washing operations entail exposure of personnel to radioactivity.
A second method for recovery of fluorine-18 from a reaction chamber such as described herein is by the use of a carrier gas. The most common such gases are fluorine, hydrogen fluoride and nitrous oxide. These gases undergo a reaction in the vessel and are taken out as .sup.18 F-F.sub.2, H.sup.18 F and NO.sup.18 F, respectively. The use of such gases is characterized by somewhat lower yields than other ways of recovering .sup.18 F. More important is the problem of the scavenger or carrier gas itself, i.e. how to handle and dispose of it after the product has been removed, particularly in the instance of HF and F.sub.2 wherein there is a toxicity problem.
In accordance with the present invention, a method has been discovered whereby fluorine-18 can be recovered from a reaction vessel in ultrapure form with substantially no radiocontaminants utilizing a carrier free system and with a minimum potential exposure of personnel to radioactivity .